Various modulation methods have been used to transmit a signal in both wireless communication and wire communication. One known signal modulation is pulse-position modulation (PPM).
In a PPM signal, when a signal level at given times from a reference point is encoded so as to go high (H) and low (L) in that order, this represents 0. When a signal level at given times from the reference point is encoded so as to go low (L) and high (H) in that order, this represents 1.
To reproduce the PPM signal reliably, it is necessary to sample the PPM signal accurately. In the process of transmitting the PPM signal, the pulse position varies. Accordingly, even if the PPM signal is sampled with a specific sampling period, there is a possibility that the PPM signal cannot be reproduced accurately due to a variation in the pulse position.
Jpn. Pat. Appln. KOKAI Publication No. 6-216778 has disclosed the configuration of an apparatus which compares the durations of the high (H) level/low (L) level of predetermined transmit data with the durations of the H level/L level of measured transmit data and adjusts the sampling timing according to the comparison result.